Study On The Structure And Properties Of In-situ Alloys Of Polypropylene Modified By Low Temperature Plasma With Polystyrene

A new method was applied to prepare in-situ alloys of polypropylene modifiedby low temperature plasma with Polystyrene. At the same time PP/PS physical blendsof the same proportion as PP/PSt alloys were prepared by a torque rheometer forcomparison.A self-designed glow discharge plasma apparatus was set up and itsperformances were investigated. Plasma treated such carbon dioxide(CO2)and CO2mixed with styrene were used to treat PP films surface.DPPH method was used todetermine the concentration of free radicals on the treated melted PP films surface andthe surface elements content as well as oxygen-containing groups after plasmatreating were characterized by X-ray photoelectron spectroscopy(XPS). Fouriertransform infrared spectroscopy(FTIR) was also used to characterize depositionsediment of styrene and CO2plasma. Based on the studies above, a working conditionwas determined:bath temperature should be55℃, lectrode distance should be2.6cm,CO2was used as the plasma gas source,and plasma treating condition should be35V,15minutes.Scanning electron microscopy (SEM) was used to characterize the morphologyof the PP/PSt alloys and PP/PS physical blends.A rotary rheometer was used to obtainthe viscosity, storage modulus, loss modulus and complex modulus of thesamples.According to SEM, DSC and rheometer studies, it can be concluded thatargon plasma of dielectric barrier discharge(DBD) treated PP particles in advance andthe use of glow discharge of CO2mixing styrene plasma treated melted PP will helpto improve the compatibility of PP/PS blends.According to SEM,DSC,FTIR,TG results, PP-g-PSt was formed in the alloys andthe interface of PPP/PSt alloys was not sharp regardless of the PP as the continuousphase or PS as continuous phase.So it can be concluded that the two phases in alloysare partially compatibile.The crystallization process of PP/PS blends and PPP/PStalloys were investigated by POM and rheometer, PP-g-PSt of PPP/PSt alloys did notplay a role in the nucleation, but reduced crystallization rate of PP of the alloys. Timesweep tests with costant frequency of1Hz showed that the nucleation rate of PP/PSblends was faster compared with PP when PS composition did not exceed60%andPS played the role of a nucleating agent. In PPP/PSt alloys, PP and PSt have strongerinterfacial interactions, PSt did not play the role of a nucleating agent and thepresence of PSt and PP-g-PSt hindered crystallization of PP greatly.